“Thin client” technologies are commonly used to prevent information leaks and to reduce operation and maintenance costs of personal computers (PCs). In a thin client system, clients have minimum functions and a server manages resources such as applications and files.
In such a thin client system, although the server actually executes processes and causes the clients to display the results of the processes and data stored in the server, it appears as if the clients themselves execute the processes and store the data.
For example, in a thin client system, a server executes business applications such as a word processor and a mailer, and causes clients to display the processing results of the business applications. Here, it is desired to use a wider range of applications in a thin client system in addition to business applications as described above. Examples of such applications include an application (e.g., a computer-aided design (CAD) application) for processing detailed images and an application for processing videos.
However, when large-volume data such as images and videos are transmitted via a protocol such as a Remote Desktop Protocol (RDP) or a Remote Frame Buffer (RFB) protocol for Virtual Network Computing (VNC) used for communications in a thin client system, the response time of operations performed at clients increases. This problem occurs not only in processes involving transmission of images and videos, but in any process involving transmission of high-volume data for screen updates between a client and a server in a thin client system.
Japanese Laid-Open Patent Publication No. 2006-236046 discloses a technology where a server generates a current pointer (or key input information) when a delay occurs at the server and sends the generated current pointer as screen data to a client to allow the user to determine the cause of the delay at the client.
Japanese Laid-Open Patent Publication No. 2009-075808 discloses a technology where events are filtered based on the number of operations and time intervals and combined based on their types to reduce the number of events and thereby enable a server to efficiently process a large number of events.
Japanese Laid-Open Patent Publication No. 03-218512 discloses a technology where some mouse movement events are removed at a predetermined rate to reduce the load of draw processing when a large number of mouse movement commands are generated. Japanese Laid-Open Patent Publication No. 2000-158727 discloses a technology for an image output system where a threshold for determining whether to perform pre-rendering for a current process is changed according to a period of time taken for a previous rendering process.